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50w Single-Ended BAF2015 Schade Enabled
50w Single-Ended BAF2015 Schade Enabled
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Old 5th August 2018, 06:21 PM   #611
dmy is offline dmy  United States
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Quote:
Originally Posted by analog_sa View Post
Do you have a capacitor in parallel to the switch?
No I did not put a cap there. I should try that. Thanks
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Old 6th August 2018, 07:22 PM   #612
Soundhappy is offline Soundhappy  France
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Quote:
Originally Posted by dmy View Post
....I do not have low output Z preamps all other pres are in the 1k - 1.5k range.
I did not bother to try them I am afraid the result would be similar.
I need a capable preamp.....

What preamp do you use to drive the Schade?
@ Dmy

Life is easy if between tube preamp and Schade 50W You install jfet's impedance buffer.
Every preamp output ~ 1.5K with the buffer together become 25 Ohm and give excellent frequency response from DC to ~ 200KHz.
It's single-ended 50 watt's and 20 dB of gain from IXYS mosfet
so no need for lot of more gain from preamp if good quality audio source
DAC or CD player ( no gadget : tablet's , smartphone etc. ).
Input transformers sound performance of Jensen and Cinemag is highly recommended or similar ( better ?)
Worse input transormers roll off low and high frequency and bring more distorsion to the music.
Do Your input transformers specyfications datasheet are garantie OK for an audio power amplifier ??
Schematic source : First Watt
Best regards
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Old 6th August 2018, 09:33 PM   #613
dmy is offline dmy  United States
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I used this input transformer in a DAC before, it is not the transformer that roll off the freq.

The circuit you provided below, can the DC be kept at 0v all the time? It does not employ cap to block DC any DC at the output will saturate the input transformer though.
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Old 6th August 2018, 09:55 PM   #614
Soundhappy is offline Soundhappy  France
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Matched 2SK170 | 2SJ74 pairs with Ids ~ 8.2 mA is ideal
but trimmer do the job if not perfect match and you get 0V DC all the time, +- 12V buffer PSU is regulated, stabilized
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Old 6th August 2018, 10:18 PM   #615
Soundhappy is offline Soundhappy  France
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More informations about impedance buffer | passive preamlifier is in Papa article :

http://www.firstwatt.com/pdf/prod_b1_man.pdf

B1 Rev.1 output impedance = 50 Ohm so Schade amp can go -3 dB 100 kHz at high frequency.

This version is build with 4 pcs. of 2SK170 BL grade and have 10 uF electochemical capacitors at the output.

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Old 6th August 2018, 11:20 PM   #616
dmy is offline dmy  United States
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Thank you, Soundhappy. I will keep this in mind. The DIY audio store is currently out of the transistors
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Old 6th August 2018, 11:47 PM   #617
Soundhappy is offline Soundhappy  France
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This is verified genuine Toshiba seller , write him message about jfet's Idss=8.2 mA matched pairs.
Genuine Toshiba 2SK170BL/2SJ74BL high transconductance JFET complimentary pair | eBay

Perfect for the buffer no worry if little mismatch after all trimmer help to get 0V DC.

or this one Punkydawgs shop with tighty matched pairs but at higher price
Toshiba 2SJ74 + 2SK170 LAB MATCHED QUAD to 0.03mA AND 4mV (7ma range) | eBay

Greetings
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Old 7th August 2018, 10:21 PM   #618
dmy is offline dmy  United States
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Will look into building the buffer. Thanks.
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